I couldn't help but tear up, damn... That's too cruel Yi-hwa... She made me feel bad for her a few chapters ago, but whatever the reason for her sudden disappearance was, that's just cruel.
I think Yi-hwa's mom didnt approve, judging from how she had a 180 in attitude towards her. Maybe an ultimatum of sorts and Yi-hwa had no way to handle it.
That and maybe the I Love You. With her moms flippant attitude towards love maybe there is some trauma there that scared Yi-hwa